A method for widening the heat treatment process window of high magnetic permeability nanocrystalline ribbons

Abstract

The present invention relates to the field of magnetic material preparation and heat treatment technology, specifically a method for widening the heat treatment process window of a high magnetic permeability nanocrystalline strip. By gradient composition design and pulsed magnetic field coupling heat treatment, the initial magnetic permeability of the strip exceeds 220,000 and the heat treatment temperature range is widened to 400°C-600°C; the alloy composition is Fe73.5%, Cu1%, Nb3%, Si13.5%, B8.5%, Co0.5%, and during heat treatment, the temperature is first raised to 450°C at 15°C / min and a 0.8T pulsed magnetic field is applied to keep the temperature, and then the temperature is raised to 550°C for keeping the temperature, crystallizing to generate α-Fe(Si) nanocrystals and Co-B amorphous interface phase, with Co distributed in the form of solid solution. This method widens the heat treatment temperature range, improves the initial magnetic permeability of the strip, improves toughness to meet automated production, and reduces costs using existing equipment; the prepared strip has high magnetic permeability and good stability, is suitable for a variety of scenarios, and has good economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic material preparation and heat treatment, in particular to a method for widening the heat treatment process window of a high-magnetic-permeability nanocrystalline ribbon. Background Art

[0002] Nanocrystalline soft magnetic materials, as a new type of soft magnetic material, possess excellent properties such as high saturation induction, low loss, and high permeability. my country's nanocrystalline soft magnetic materials industry has established a complete industrial chain from material preparation to device production, covering high-, mid-, and low-end products. Currently, there are over 50 nanocrystalline ribbon manufacturers both domestically and internationally, with a total global production capacity of nearly 48,000 tons. However, actual demand is approximately 31,000 tons, leaving a significant gap between production capacity and demand.

[0003] Existing nanocrystalline ribbons face numerous challenges in their application. The brittle ribbons used in current transformers suffer from severe breakage during the winding process, hindering industrial automation. Traditionally, high initial permeability materials are achieved through high Nb, Si, and B content. However, high Nb content hinders mass production on amorphous units, while high Si and B content lead to brittle ribbons, increasing breakage rates and preventing continuous production. Furthermore, the existing heat treatment process window is narrow, making it difficult to meet the demands of mass production.

[0004] To address these challenges, the present invention proposes a method for broadening the heat treatment process window for high-permeability nanocrystalline ribbons. By optimizing alloy composition and heat treatment parameters, batch production is achieved on amorphous mills, widening the heat treatment temperature range and improving the ribbon's toughness, meeting automated production requirements and filling a gap in equipment capacity. Summary of the Invention

[0005] (1) Technical problems solved

[0006] In view of the deficiencies of the prior art, the present invention provides a method for widening the heat treatment process window of high magnetic permeability nanocrystalline ribbons.

[0007] (2) Technical solution

[0008] A method for widening the heat treatment process window of high permeability nanocrystalline ribbons is proposed. By coupling gradient composition design with pulsed magnetic field heat treatment, the initial magnetic permeability of the ribbon is greater than 220,000 and the heat treatment temperature range is widened to 400°C-600°C. The alloy composition is Fe73.5%, Cu1%, Nb3%, Si13.5%, B8.5%, and Co0.5% in atomic percentage. During heat treatment, the temperature is first raised to 450°C at 15°C / min and a 0.8T pulsed magnetic field is applied for 40 minutes. The temperature is then raised to 550°C at 8°C / min and kept for 90 minutes. The crystallization reaction formula is: Fe 73.5 CuNb3Si 13.5 B 8.5 Co 0.5Amorphous phase → α-Fe(Si) nanocrystals + Co-B amorphous interface phase, in which Co is distributed in the α-Fe lattice gap in the form of atomic-level solid solution.

[0009] Preferably, a gradient temperature field on the surface of the copper roller is used during double-roller rapid quenching, so that the Nb content in the cross section of the strip decreases linearly from 5% in the surface layer to 3% in the core layer, forming a 5μm thick surface high Nb barrier layer to inhibit abnormal grain growth, and at the same time, the Si content decreases linearly from 14% in the surface layer to 13% in the core layer.

[0010] Preferably, the method further includes controlling the magnetic field direction to form a 30° angle with the strip rolling direction during the pulsed magnetic field heat treatment, and inducing the magnetic domain orientation to be uniform by the Lorentz force, so that the magnetocrystalline anisotropy energy is reduced to 8×10 -4 J / m³, corresponding to a coercive force ≤0.08A / m, and a mixed gas containing N2-8%H2 was introduced during the insulation stage to form a 3nm thick Fe4N nano-coating on the surface of the strip.

[0011] Preferably, 0.3% rare earth element Gd is added during alloy smelting to form an intermetallic compound nucleation core with the chemical formula of GdFe3, which is preferentially precipitated in the early stage of crystallization, increasing the density of nanocrystalline cores to 1.5×10 20 pcs / m 3 At the same time, vacuum induction melting was used to produce 18μm thick amorphous strip with a lamination coefficient ≥0.88.

[0012] Preferably, ultrasonic vibration with a power of 400 W and a frequency of 25 kHz is introduced during the heat treatment heating stage to generate a microstress field inside the strip through the acoustic cavitation effect, thereby promoting the diffusion of B atoms to the grain boundaries to form a 2.5 nm thick B-rich interface phase, and increasing the grain boundary resistance by 60%. At the same time, the segmented annealing processes are: 400°C for 30 minutes; 520°C for 30 minutes; and 580°C for 15 minutes.

[0013] Preferably, the Cu element in the alloy is distributed in the amorphous matrix in the form of nanoclusters with a diameter of 4 nm. High-resolution transmission electron microscopy observation shows that there is a 1.2 nm thick Cu-Fe-Si disordered transition layer at the interface with the α-Fe nanocrystal, which reduces the interface magnetoresistance by 25%. After heat treatment, a 1.2 μm thick Ni 0.6 Zn 0.4 The spinel structure of Fe2O4 ferrite film forms a magnetoelectric coupling layer with the nanocrystalline ribbon, and the magnetic permeability retention rate is ≥88% at 100kHz.

[0014] Preferably, the heat treatment window is determined by differential scanning calorimetry to be the exothermic peak range of 470°C-540°C, the crystallization activation energy Ea in this range is 290-310 kJ / mol, and the crystallization index n is calculated by the Kissinger equation to be 1.9, indicating that the crystallization is mainly two-dimensional growth, and the magnetic permeability fluctuation is ≤2.5% when the heating rate fluctuates by ±2°C / min.

[0015] Preferably, after heat treatment, the strip is surface-insulated to form a 1.5 μm thick MgO-SiO2 composite insulation layer with a withstand voltage of ≥600V, and the initial magnetic permeability is detected by an LCR tester at 1kHz and 0.5mT, and the magnetic permeability fluctuation in the temperature range of 450℃-550℃ is ≤4%.

[0016] Preferably, the B content in the alloy composition is adjusted to 8.5% and 0.5% Co is added. X-ray photoelectron spectroscopy confirms that Co is Co 2+ It forms a solid solution in the α-Fe lattice, increasing the saturation magnetic induction to 1.3T, while the Nb element inhibits grain growth.

[0017] Preferably, square wave pulses are used during pulsed magnetic field heat treatment, and magnetic fields parallel and perpendicular to the strip surface are applied alternately during the holding stage to induce the nanocrystals to <100> The crystal orientation is preferred, and the degree of orientation is confirmed to be above 85% by pole figure analysis, and the corresponding temperature coefficient of magnetic permeability is ≤150ppm / ℃.

[0018] (3) Beneficial technical effects

[0019] Compared with the existing technology, the beneficial effects of the present invention are:

[0020] 1. By optimizing the alloy composition and adopting a gradient design, the initial magnetic permeability of the strip is greater than 180,000, meeting the high magnetic permeability requirement and solving the preparation difficulties caused by the traditional high Nb content.

[0021] 2. Expanding the heat treatment temperature range to 450°C-550°C improves process flexibility, adapts to different production conditions, and improves production efficiency. Auxiliary methods such as pulsed magnetic fields and ultrasonic vibrations are introduced into the heat treatment process to promote uniform precipitation of nanocrystals, refine grain size, reduce coercivity, and improve magnetic permeability stability.

[0022] 3. By adjusting the composition and optimizing the process, the strip toughness is improved, the breakage rate is reduced, and the requirements for automated winding are met. This method fully utilizes the existing amorphous unit capacity, eliminating the need for additional equipment investment, reducing production costs, and achieving excellent economic and social benefits. The strip produced by this method has a high lamination coefficient and is suitable for a variety of applications, such as current transformers and high-frequency transformers, broadening the application range of nanocrystalline strip. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of a method for widening the heat treatment process window of high magnetic permeability nanocrystalline ribbons proposed in the present invention;

[0024] Figure 2 2. It is a comparison chart of the initial magnetic permeability of the embodiment and the comparative example;

[0025] Figure 3 is a comparison diagram of saturation magnetic induction and coercive force of the embodiment and the comparative example;

[0026] Figure 4 It is a columnar comparison chart of the lamination coefficient of the embodiment and the comparative example. DETAILED DESCRIPTION

[0027] according to Figures 1 to 4 , the specific implementation methods of the present invention are as follows:

[0028] Example 1: Preparation of high magnetic permeability nanocrystalline ribbons by gradient composition coupled with pulsed magnetic field heat treatment

[0029] S1. Alloy composition design and smelting

[0030] The atomic percentages are Fe73.5%, Cu1%, Nb3%, Si13.5%, B8.5%, and Co0.5%. Accurately weigh pure iron (purity ≥99.9%), electrolytic copper (purity ≥99.95%), ferroniobium alloy (Nb content ≥65%), crystalline silicon (purity ≥99.5%), ferroboron alloy (B content ≥20%), and cobalt powder (purity ≥99.9%). A three-stage vacuum induction melting furnace is used for smelting, and the vacuum level in the furnace is maintained at 1×10 -3 Pa below, the melting temperature was controlled at 1550°C and held for 25 minutes to ensure full melting of the alloying elements and uniform composition. The melt was poured through a quartz nozzle onto a rotating copper roller (300mm diameter, 25m / s) with a chrome-plated surface. It was rapidly cooled through a gradient temperature field on the copper roller surface (a 50°C temperature difference between the center and edge of the roller surface) to produce an 18μm thick amorphous strip. The cross-section of the strip exhibited a gradient distribution of Nb and Si: the Nb content in the surface layer decreased linearly from 5% to 3% in the core layer within 5μm, while the Si content decreased from 14% in the surface layer to 13% in the core layer. This gradient design allows the formation of a high-Nb barrier layer on the surface during subsequent crystallization, effectively inhibiting abnormal grain growth.

[0031] S2. Pulsed magnetic field assisted heat treatment

[0032] The amorphous strip is placed in a vacuum annealing furnace and heat treated in two stages:

[0033] The first heating stage: The temperature is raised to 450°C at a rate of 15°C / min while a mixture of N₂ and 8% H₂ is introduced, with the pressure maintained at 0.2 MPa. After reaching the target temperature, a 0.8T square-wave pulsed magnetic field (100Hz frequency, 60% duty cycle) is applied, with the magnetic field directed at a 30° angle to the rolling direction, and the temperature is maintained for 40 minutes. This magnetic field parameter induces uniform magnetic domain orientation through the Lorentz force, reducing magnetocrystalline anisotropy.

[0034] The second heating stage: the temperature is raised to 550°C at a rate of 8°C / min, a pulsed magnetic field is continuously applied and held for 90 minutes, followed by furnace cooling to room temperature at a rate of 5°C / min. Throughout the heat treatment, a 400W, 25kHz ultrasonic vibration device is simultaneously activated to generate a microstress field within the strip through the acoustic cavitation effect, promoting the diffusion of boron atoms to the grain boundaries.

[0035] S3. Surface insulation treatment

[0036] The insulating layer is deposited on the surface of the strip using magnetron sputtering technology: Ni 0.6 Zn 0.4 Fe2O4 ferrite was used as the target, with a sputtering power of 150W, an argon pressure of 0.5Pa, and a deposition temperature of 200°C to produce a 1.2μm thick ferrite film. This film forms a magnetoelectric coupling layer with the nanocrystalline ribbon, improving the stability of the magnetic permeability under high-frequency conditions.

[0037] S4. Performance Testing

[0038] Magnetic permeability test: Using a HIOKI 3532-50 LCR meter, at a frequency of 1 kHz and an excitation of 0.5 mT, the initial magnetic permeability of the strip was measured to be μi = 225,000. The magnetic permeability fluctuated by only 3.2% in the temperature range of 450°C-550°C.

[0039] Microstructure analysis: JEOL-2100F high-resolution transmission electron microscope observation shows that the average size of α-Fe(Si) nanocrystals is 8.5nm, and there is a 2.5nm thick B-rich interface phase at the grain boundary, which effectively isolates the grains and reduces the resistance to magnetic domain wall movement.

[0040] Magnetic properties test: The coercive force Hc was measured to be 0.07A / m by vibrating sample magnetometer, and the magnetocrystalline anisotropy was 7.8×10 -4 J / m 3 , indicating that the magnetic domain orientation is well uniform.

[0041] Example 2: Process Optimization of Rare Earth Gd Addition and Segmented Annealing

[0042] S1. Alloy Melting and Strip Preparation

[0043] To the alloy composition of Example 1, 0.3 atomic percent rare earth element Gd (purity ≥99.99%) was added. The alloy was heated in a vacuum induction melting furnace at 1580°C for 30 minutes. The melt was then poured through a quartz nozzle onto a rotating copper roller (rotating at 25 m / s) to produce an 18-μm-thick amorphous ribbon. The Nb content in the ribbon cross section decreased linearly from 5% in the surface layer to 3% in the core layer, and the Si content decreased from 14% in the surface layer to 13% in the core layer, achieving a lamination coefficient of 0.88. The addition of the rare earth element Gd forms GdFe3 intermetallic compound nucleation cores during the initial crystallization phase, increasing the density of the nanocrystal nuclei.

[0044] S2. Segmented annealing process

[0045] Stage S1: The temperature is raised to 400°C at a rate of 12°C / min, and a N2-8% H2 mixture (at a pressure of 0.18 MPa) is introduced for 30 minutes. During this stage, the degree of crystallization reaches 25%, and GdFe3 nucleation cores are preferentially precipitated, providing uniform nucleation sites for subsequent crystallization.

[0046] Stage S2: The temperature is raised to 520°C at a rate of 6°C / min. A 0.7T pulsed magnetic field (80Hz frequency) is applied, with the magnetic field at a 35° angle to the rolling direction, for 30 minutes. The crystallinity is increased to 80%, and the pulsed magnetic field induces the preferential growth of nanocrystals.

[0047] S3 stage: heat to 580℃ at a rate of 10℃ / min, stop applying the magnetic field, keep warm for 15 minutes, make the degree of crystallization ≥98%, then introduce high-purity nitrogen (flow rate 10L / min) and quickly cool to room temperature to avoid high-temperature grain coarsening.

[0048] S3.Surface treatment and testing

[0049] A 1.5μm-thick MgO-SiO2 composite insulating layer was deposited using magnetron sputtering technology, with an MgO target power of 100W and a SiO2 target power of 80W. The resulting insulating layer has a withstand voltage of ≥650V. Differential scanning calorimetry (DSC) testing determined the exothermic peak range to be 475°C-535°C, with a crystallization activation energy Ea of 295kJ / mol. Using the Kissinger equation, the crystallization index n=1.85 was calculated, indicating that the crystallization is primarily a two-dimensional growth mode and excellent process stability.

[0050] Example 3: Co content optimization and magnetic domain orientation control

[0051] S1. Alloy composition adjustment

[0052] The Co content was increased to 1 atomic percent, the B content was reduced to 8%, and the remaining components were configured as follows: Fe 73.5%, Cu 1%, Nb 3%, and Si 13.5% by atomic percentage. A vacuum induction melting furnace was maintained at 1560°C for 25 minutes, and the melt was cast onto a rotating copper roller (28 m / s) to produce a 16μm-thick amorphous ribbon. The ribbon cross-section showed a Nb content of 5.2% in the surface layer and 2.8% in the core layer. The Si content decreased gradually from 14.2% in the surface layer to 12.8% in the core layer, enhancing the surface grain suppression effect.

[0053] S2. Pulsed magnetic field heat treatment

[0054] Heating stage: the temperature was raised to 450℃ at a rate of 18℃ / min, and a 0.9T pulsed magnetic field (frequency 120Hz, duty cycle 70%) was applied. The direction of the magnetic field was alternately parallel and perpendicular to the strip surface every 10 minutes. The temperature was kept for 50 minutes to induce the nanocrystals to grow along the strip surface. <100> Preferred crystal orientation.

[0055] Heating and Cooling: The temperature was raised to 540°C at a rate of 7°C / min, a pulsed magnetic field was continuously applied and the temperature was maintained for 80 minutes, followed by cooling to room temperature at a rate of 6°C / min. Ultrasonic vibration at 350W and 22kHz was simultaneously activated during the heat treatment to promote uniform diffusion of Co atoms.

[0056] S3. Performance Characterization

[0057] Composition and structure analysis: X-ray photoelectron spectroscopy (XPS) confirmed that Co 2+ The nanocrystals are dissolved in the α-Fe lattice, and the saturation magnetic induction is increased to 1.32 T. The pole figure analysis shows that the nanocrystals are <100> The crystal orientation degree reaches 87%, and the temperature coefficient of magnetic permeability is 140ppm / ℃ (-40℃-120℃).

[0058] Magnetic performance test: Using an LCR meter, the initial magnetic permeability measured at 1kHz and 0.5mT is 230,000, and the high-frequency magnetic permeability retention rate (100kHz) is ≥88%, meeting the requirements of wide temperature range and high-frequency applications.

[0059] Comparative example: Traditional uniform composition heat treatment without magnetic field

[0060] S1. Alloy Preparation

[0061] A 20μm thick amorphous strip with a uniform composition of Fe73.5%, Cu1%, Nb3%, Si13.5%, and B9% (no Co addition) was produced at a melting temperature of 1500℃ and rapid quenching with a copper roller, without a composition gradient distribution.

[0062] S2. Conventional annealing treatment

[0063] The temperature was raised to 500°C in an air furnace at 10°C / min, kept at this temperature for 60 min, and then air-cooled to room temperature without applying a magnetic field or ultrasonic vibration.

[0064] The performance test results of the embodiments and comparative examples are shown in the following table:

[0065] Table 1

[0066] Performance indicators Example 1 Example 2 Example 3 Comparative Example Initial magnetic permeability (10,000) 22.5 23.1 23.0 15.2 Magnetic permeability temperature fluctuation (450-550℃) ≤3.2% ≤2.8% ≤3.0% ≤8.5% Saturation magnetic induction (T) 1.30 1.29 1.32 1.25 Coercive force (A / m) 0.07 0.06 0.05 0.52 Grain size (nm) 8.5±1.2 7.8±0.9 7.5±1.1 15.3±2.3 Lamination coefficient 0.88 0.89 0.87 0.80

[0067] The surface high Nb barrier layer of Examples 1-3 reduces the grain size by 40%-50%, inhibiting abnormal growth, while the control example has coarse grains due to uniform composition and significantly reduces the magnetic permeability. The 30°-35° magnetic field angle increases the magnetic domain orientation to more than 85%, and reduces the coercive force by 85%. The absence of a magnetic field in the control example leads to disordered magnetic domains, with a coercive force of 0.52A / m. In Example 2, the GdFe3 intermetallic compound increases the nucleus density by 3 times, the degree of crystallization reaches 98%, and the heat treatment window is widened to 400℃-580℃, verifying the optimization of crystallization kinetics by rare earth addition. In Example 3, Co 2+ Solid solution increases the saturation magnetic induction by 5.6%. At the same time, the Fe4N coating (3nm) and the ferrite film synergistically improve the temperature stability of the magnetic permeability, with fluctuations in the range of -40℃-120℃ ≤5%.

[0068] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for widening the heat treatment process window of high permeability nanocrystalline ribbons, characterized by: Through gradient composition design and pulsed magnetic field coupling heat treatment, the initial magnetic permeability of the strip is greater than 220,000 and the heat treatment temperature range is widened to 400℃-600℃; the alloy composition is Fe73.5%, Cu1%, Nb3%, Si13.5%, B8.5%, Co0.5% in atomic percentage. During the heat treatment, the temperature is first raised to 450℃ at 15℃ / min and a 0.8T pulsed magnetic field is applied for 40 minutes, then the temperature is raised to 550℃ at 8℃ / min and the temperature is kept for 90 minutes. The crystallization reaction formula is: Fe 73.5 CuNb3Si 13.5 B 8.5 Co 0.5 Amorphous phase → α-Fe(Si) nanocrystals + Co-B amorphous interface phase, in which Co is distributed in the α-Fe lattice gap in the form of atomic-level solid solution.

2. The method for widening the heat treatment process window of high permeability nanocrystalline ribbon according to claim 1, characterized in that: It also includes the use of a gradient temperature field on the surface of the copper roller during double-roller rapid quenching, so that the Nb content in the cross-section of the strip decreases linearly from 5% in the surface layer to 3% in the core layer, forming a 5μm thick surface high-Nb barrier layer to inhibit abnormal grain growth. At the same time, the Si content decreases linearly from 14% in the surface layer to 13% in the core layer.

3. The method for widening the heat treatment process window of high magnetic permeability nanocrystalline ribbon according to claim 1, characterized in that: The method also includes controlling the magnetic field direction to form a 30° angle with the strip rolling direction during pulsed magnetic field heat treatment, and inducing the magnetic domain orientation to be uniform through the Lorentz force, so that the magnetocrystalline anisotropy energy is reduced to 8×10 -4 J / m³, corresponding to a coercive force ≤0.08A / m, and a mixed gas containing N2-8%H2 was introduced during the insulation stage to form a 3nm thick Fe4N nano-coating on the surface of the strip.

4. The method for widening the heat treatment process window of high permeability nanocrystalline ribbon according to claim 1, characterized in that: 0.3% rare earth element Gd is added during alloy smelting to form an intermetallic compound nucleation core with the chemical formula of GdFe3, which precipitates preferentially at the initial stage of crystallization, increasing the density of nanocrystalline cores to 1.5×10 20 pcs / m 3 At the same time, vacuum induction melting was used to produce 18μm thick amorphous strip with a lamination coefficient ≥0.

88.

5. The method for widening the heat treatment process window of high permeability nanocrystalline ribbon according to claim 1, characterized in that: During the heat treatment heating stage, ultrasonic vibration with a power of 400W and a frequency of 25kHz was introduced to generate a microstress field inside the strip through the acoustic cavitation effect, prompting B atoms to diffuse to the grain boundaries to form a 2.5nm thick B-rich interface phase, which increased the grain boundary resistance by 60%. At the same time, the segmented annealing processes were as follows: 400℃ for 30 minutes; 520℃ for 30 minutes; and 580℃ for 15 minutes.

6. The method for widening the heat treatment process window of high permeability nanocrystalline ribbon according to claim 1, characterized in that: The Cu element in the alloy is distributed in the amorphous matrix in the form of nanoclusters with a diameter of 4nm. High-resolution transmission electron microscopy observation shows that there is a 1.2nm thick Cu-Fe-Si disordered transition layer at the interface with the α-Fe nanocrystal, which reduces the interfacial magnetic resistance by 25%. After heat treatment, a 1.2μm thick Ni 0.6 Zn 0.4 The spinel structure of Fe2O4 ferrite film forms a magnetoelectric coupling layer with the nanocrystalline ribbon, and the magnetic permeability retention rate is ≥88% at 100kHz.

7. The method for widening the heat treatment process window of high permeability nanocrystalline ribbon according to claim 1, characterized in that: Differential scanning calorimetry determined that the heat treatment window was the exothermic peak range of 470℃-540℃. The crystallization activation energy Ea in this range was 290-310kJ / mol. The crystallization index n was calculated by the Kissinger equation to be 1.9, indicating that the crystallization was mainly two-dimensional growth, and the magnetic permeability fluctuation was ≤2.5% when the heating rate fluctuated by ±2℃ / min.

8. The method for widening the heat treatment process window of high permeability nanocrystalline ribbon according to claim 1, characterized in that: After heat treatment, the strip undergoes surface insulation treatment to form a 1.5μm thick MgO-SiO2 composite insulation layer with a withstand voltage of ≥600V. The initial magnetic permeability is tested by an LCR tester under 1kHz and 0.5mT conditions, and the magnetic permeability fluctuation is ≤4% in the temperature range of 450℃-550℃.

9. The method for widening the heat treatment process window of high permeability nanocrystalline ribbon according to claim 1, characterized in that: The B content in the alloy was adjusted to 8.5% and 0.5% Co was added. X-ray photoelectron spectroscopy confirmed that Co was dissolved in the α-Fe lattice in the form of Co²⁺, increasing the saturation magnetic induction to 1.3T. At the same time, the Nb element suppressed grain growth.

10. The method for widening the heat treatment process window of high permeability nanocrystalline ribbon according to claim 1, characterized in that: Square wave pulses are used in pulsed magnetic field heat treatment. During the holding stage, magnetic fields parallel and perpendicular to the strip surface are applied alternately to induce the nanocrystals to <100> The crystal orientation is preferred, and the degree of orientation is confirmed to be above 85% by pole figure analysis, and the corresponding temperature coefficient of magnetic permeability is ≤150ppm / ℃.

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